This invention relates to a glass enamel composition which is a composition that includes ceramic coloring agents and can be fired upon a glass substrate. Typically, the glass enamel composition is comprised of very finely divided oxides in a oil and resin carrier-binder that can be applied to the glass substrate by silk screening, rolling or painting.
For some years automobiles have been supplied with rear windows (called "backlites" in the automobile industry) printed with an electrically conductive glass-metal grid composed of vertical bus bars and very fine horizontal lines running across the window. The conductive glass-metal grid is, for example, applied by silk screening upon the window a composition comprising very fine silver powder and a finely ground soft lead glass dispersed in an oil and resin carrier. The windows are then heated to a temperature at which the soft lead glass melts and the silver grid is permanently fixed to the surface of the glass window.
In recent years, to improve the appearance of the backlites and to protect materials that secure the edges and the backlites from radiation, a dark grey or black border of glass enamel has been printed around the edge of the glass. In some cases, the conductive glass-metal coatings have been applied over the glass enamel. In other cases, the glass-metal coatings have been applied abutting the glass enamel border. When the conductive coating is applied over the grey or black glass enamel and after firing, it shows through as a discoloration. Where the conductive coating abuts the glass enamel border, an interaction between the two is visibly apparent. The interaction between the conductive coatings and the glass enamels, whether overlapping or abutting, is not only unsightly but appears to reduce the electrical conductivity of the conductive coating and appears to reduce the strength of solder connections between the coatings and electrical lead wires.